avc_has_perm

Section: SELinux API documentation (3)
Updated: 27 May 2004
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NAME

avc_has_perm, avc_has_perm_noaudit, avc_audit, avc_entry_ref_init - obtain and audit SELinux access decisions.

SYNOPSIS

#include <selinux/selinux.h>

void avc_entry_ref_init(struct avc_entry_ref *aeref);

int avc_has_perm(security_id_t ssid, security_id_t tsid, security_class_t tclass, access_vector_t requested,

struct avc_entry_ref *aeref, void *auditdata);

int avc_has_perm_noaudit(security_id_t ssid, security_id_t tsid, security_class_t tclass, access_vector_t requested,

struct avc_entry_ref *aeref, struct av_decision *avd);

void avc_audit(security_id_t ssid, security_id_t tsid, security_class_t tclass, access_vector_t requested,

struct av_decision *avd, int result, void *auditdata);

DESCRIPTION

avc_entry_ref_init initializes an avc_entry_ref structure; see ENTRY REFERENCES below. This function may be implemented as a macro.

avc_has_perm checks whether the requested permissions are granted for subject SID ssid and target SID tsid, interpreting the permissions based on tclass and updating aeref, if non-NULL, to refer to a cache entry with the resulting decision. The granting or denial of permissions is audited in accordance with the policy. The auditdata parameter is for supplemental auditing; see avc_audit below.

avc_has_perm_noaudit behaves as avc_has_perm without producing an audit message. The access decision is returned in avd and can be passed to avc_audit explicitly.

avc_audit produces an audit message for the access query represented by ssid, tsid, tclass, and requested, with a decision represented by avd. Pass the value returned by avc_has_perm_noaudit as result. The auditdata parameter is passed to the user-supplied func_audit callback and can be used to add supplemental information to the audit message; see avc_init(3).

ENTRY REFERENCES

Entry references can be used to speed cache performance for repeated queries on the same subject and target. The userspace AVC will check the aeref argument, if supplied, before searching the cache on a permission query. After a query is performed, aeref will be updated to reference the cache entry for that query. A subsequent query on the same subject and target will then have the decision at hand without having to walk the cache.

After declaring an avc_entry_ref structure, use avc_entry_ref_init to initialize it before passing it to avc_has_perm or avc_has_perm_noaudit for the first time. Using an uninitialized structure will produce undefined behavior.

RETURN VALUE

If requested permissions are granted, zero is returned. If requested permissions are denied or an error occured, -1 is returned and errno is set appropriately.

In permissive mode, zero will be returned and errno unchanged even if permissions were denied. avc_has_perm will still produce an audit message in this case.

ERRORS

EACCES: A requested permission was denied.
EINVAL: The tclass and/or the security contexts referenced by ssid and tsid are not recognized by the currently loaded policy.
ENOMEM: An attempt to allocate memory failed.

NOTES

Internal errors encountered by the userspace AVC may cause certain values of errno to be returned unexpectedly. For example, netlink socket errors may produce EACCES or EINVAL. Make sure that userspace object managers are granted appropriate access to netlink by the policy.

AUTHOR

Eamon Walsh <ewalsh@tycho.nsa.gov>